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VACUUM TUBE Filed NOV. 16, 1929 INVENTOR Vladimir" if. Z wary/{277.-

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means 7 f PATE N'l ferries vacuum runs Vladimir K. Zworykin, Swissvale, Pa... assignor to Westinghouse Electric 3; Manufacturing Company, a corporation of lfennsylvania Application November 16, 1929, Serial No. 407,652

6 Claims. (01. 250-475) 4 My invention relates to vacuum tubes and it has particular relation to devices of the type known in the art as cathode-ray tubes.

Cathode-ray tubes have been utilized for many years for the measurement or the indication of electrical power, the wave-form of alternating currents or potentials, or similar conditions in electric circuits. They have also been proposed. for use in television systems, as indicated by the patent to Rosing 1,161,734. By reason of the fact, however, that it was substantially impossible to focus the cathode-ray to a well defined spot on the fluorescent screen, while still maintaining proper control of the intensity of the ray, such tubes have not, heretofore, been satisfactory as view-receiving devices.

It is, accordingly, an object of my invention to provide an improved cathode-ray tube.

Another object of my invention is to providea cathode-ray tube capable of operating under accelerating potentials of the order of thousands of volts.

Another object of my invention is to provide a cathode-ray tube of the high-vacuum type so constructed as to not require continuous pumping while in use.

Another object of my invention is to provide a cathode-ray tube in which the electrodes are simple in'construction and. have small tot'al volume, whereby their degasiflcation, by well known processes, during evacuation of the device, is facilitated.

Another object of my invention is to provide a cathode-ray tube wherein the focusing of the ray is totally unaifected by .the control-potentials.

Another object. of my invention is to provide a cathode-ray tube wherein the ray may be focused to a well defined spot.

Another. object of my invention is to provide a cathode-ray tube wherein the ray is equally well defined at all points to which it is deflected upon the fluorescent screen.

Another object of my invention is to provide a cathode-raytube wherein the accelerating potentials may be made so large in respect to the intensity-control potentials that the deflection of the ray is not influenced by the said control potentials and is the same for all intensities.

A further object of my invention ,is to provide a cathode-ray tube wherein the, electrons are accelerated in two stages, one'stage' at a'low potential and another stageat a high potential, and wherein deflection of the "electronsis accomplishedbetween the saidstagesg j, I

Still another objectof my'inve'ntion is to provide a cathode-ray-tube having such characteristics as will render it especially useful in viewtransmis'sion systems.

Specifically, acathode-ray tube, comprising a preferred embodiment of my invention, includes an electron gun constituted by a thermionic cathode, a control-electrode and a primary anode, and it also includes a conductive coating, 9. per

tion of which is fluorescent, upon the interior of the large end of the tube to constitute a secondary or accelerating anode.

I apply a very high potential between theprimary and secondary anodes, and the converging electrostatic field, set up thereby, causes the cathode-ray to be focused to a well defined spot upon the fluorescent screen.

The novel features that I consider character istic of my invention are set forth with portion larity' in the appended claims. invention itself, however, both as to its organization and its method of operation, together with additional with a reentrant press 3 through which a plural ity of lead-in elements 4, 5 and t extend and which carries a clamping' device or collar l. A plurality of rigid rods 8 extend inwardly from .the collar and carry an anode Ill constituted by a cylindrical wall portion and two circular end walls l2. A thermionic cathode is is carried by the inner ends of the lead-in elements t and is disposed closely adjacent to an opening to, ap proximately 100 mils in diameter, in the bottom ing coaxial.

The cathode is surrounded by a cup-shape shield IS. The shield is carried by one oi the lead-in elements 4 thatsupport the cathode and,

is, consequently, maintained substantially at cathode-potential. The edge of the shield is closely adjacent to the bottom of the cup-shape control-electrode i6 and, by preventing scattering of the electrons, increases the emciency of the said electrode.

One of the supports 8 of the anode I 0 is provided with an extension 20 having a cupped end portion 2i adapted to carry a small amount of getter material, such as magnesium, which is flashed during the evacuation process.

The cathode, although illustrated as being a filament, may be of the equipotential type, if desired, or of any other type capable of giving sufilcient electron emission.

A metallic deposit 22 covers the entire inner surface of the wall of the pear-shape portion 2 of the container and constitutes an accelerating, or focusing, anode. The deposit on the extreme rounded end of the tube is sufficiently thin to be translucent and over it is applied a coating 23 of fluorescent material, such as finely divided willev ing conductive material, instead of being deposited upon a conductive surface, it is highly important that the said material be connected to the accelerating-anode 22. The connection between the screen and the accelerating anode is for the purpose of carrying away the charge conveyed to it by the cathode-ray, since an. accumulated charge prevents focusing of the ray to a well defined spot.

The exact manner in which the metallic coating is applied is not important although I have found it expedient to deposit it from a solution of alkaline silver nitrate, in the manner well known to those skilled in the chemical arts. Y

A plurality of ray-deflecting devices 24 and 25 are disposed exteriorly of the vessel, intermediate the primary anode and the inner edge of the metallic deposit 22, whereby the cathode-ray may be caused to move over the fluorescent screen in any path desired.

In the operation of my improved cathode-ray tube, as a view-receiving device in a television system or the like, the first anode I0 is maintained at a positive potential of approximately -300 volts with respect to the cathode, and the metallic coating 22, on the inner wall of the tube, which constitutes the accelerating anode, is maintained at a positive potential of approximately 3,000 volts with respect thereto. The relation between the anode voltage and the voltage applied to the metallic coating is critical and I have found that, for best results, with a tube wherein the distance between the cathode and the screen 23 is approximately 20 inches, and the distance betweenthe extreme end of the anode l0 and the edge of the metallic deposit nearest thereto is about two inches, the potential of the coating should be approximately 10 times that of the anode.

When a negative potential of about 30 volts is applied to the control-electrode IS, the cathode ray is entirely blocked; potentials less negative cause variations in the intensity of the ray proportional thereto, with corresponding variations in the brilliancy of the fluorescence of the spot on the screen.

The relatively low potential required for control of the intensity of the electron stream is an important feature of my invention. It follows from the relative positioning of the cathode, the control-electrode and the anode, the dimensions of the coaxial openings therein, and the complete enclosure of the cathode by the said control-electrode, that the number of electrons, rather than their velocity, is controlled. Since the controlpotential need be only a very small fraction of the accelerating potential between the anode and the coating 22, the electron stream is not appreciably retarded thereby, and the deflection of the stream, by the devices 24 and 25, is independent of its intensity.

The control-electrode, therefore, may be utilized to impress view-frequencies upon the device,

as disclosed in my copending application, Serial No. 349,956, filed March 26th and assigned to the Westinghouse Electric 8: Manufacturing Company, while the scanning-frequencies may be impressed upon the ray-deflecting devices 24 and 25, in the manner disclosed in the same application. The tube, however, is not to be considered as limited to use in television systems, since it is also useful in electro-cardiographs, oscillographs and the like.

Under certain conditions, particularly if there is a possibility that'the ray may remain on one spot for an appreciable time, itis advisable to apply a cooling medium to the exterior of the screen. For this purpose, a transparent waterjacket may be utilized or a small fan may be mounted adjacent to the device.

In a view-receiving device, it is necessary that the fluorescent spot shall be well defined and shall have a definite diameter in order to cover properly. the distance between two adjacent scanning lines on the screen. By research and experiment, I have determined that such a spot can besecured by proper choice of the size-of the opening in the first anode and by the proper relation between the first and second potentials.

I am not, at this time, prepared to state exactly how the high positive potential applied to the metallic coating functions to assist in focusing the cathode-ray to a well defined spot. It is probable, however. that the focusing is aided by the interaction between the magnetic field setup by the moving electrons and the convergent electrostatic field through which they pass.

Furthermore, the. provision of a conductive fluorescent screen connected to the accelerating anode is an important feature of my improved cathode-ray tube, since the screen is thereby prevented from acquiring a high negative charge that would tend to repel the cathode ray and cause blurring.

It also lies within the scope of my invention to mix with the fluorescent substance a small amount of phosphorescent material or material that tends to glow for a short time after cessation of the electron impact. Such material, when incorporated into' the screen, assists materially the phenomenon of persistence of vision," permitting' a decrease in the number of frames transmitted and received per-second when the tube is utilized for the distant reproductionof motion picture films, as illustrated in my copending application hereinbefore referred to.

Although I have shown and described a specific embodiment of my invention, I am fully aware that many modifications of the structural details.

ciably decelerating it.

I claim asmy invention? 1. A cathode-ray tube including an electronsource and a first anode, a fluorescent screen and means, including said screen and a second anode adapted to be maintained at a higher voltage relative to said source than said first anode for establishing a convergent electric field around the major portion of the path traversed by an electron between said source and said screen, whereby electrons from said source may be focused to a well defined spot on said screen.

2. A cathode-ray tube comprisingan electronsource, a shield for said electron source, a control-electrode substantially enclosing said source and having a small opening in a wall thereof, a first anode having a small opening spaced from the opening in the control-electrode and in axial alignment therewith, and a second anode which is also a focusing device capable of being maintained at a high positive potential with respect to said cathode, whereby control may be had of an electron stream in said tube-without appre- 3. A cathode-ray tube comprising a container exhausted to a high vacuum, an electron-source, a shield for said electron source, a control-electrode, a first accelerating electrode and a second accelerating electrode within said container, the last named electrode being constituted by a conductive deposit upon the inner surface of the said container.

4. Electron apparatus comprising an evacuated envelope, a viewing screen at one end of the envelope, means disposed at the other end of said envelope for developing a ray of electrons and directing the same toward said screen, said means comprising a cathode, a shield for said cathode, and an anode and a control electrode interposed therebetween, said electrode being in the form of an apertured shield efiective to prevent travel of electrons from said cathode to said anode along paths around said electrode, and single anode means disposed between said screen and said first-named anode and electrically disconnected and insulated from the latter to hold a potential greater than that on said first-named anode by thousands of volts, said anode means being con-- structed and disposed to develop an electrostatic field effective to focus said ray on said screen.

5. An electron tube having a coating of electrically conductive material on the interior surface of the side wall thereof, said tube provided on an end wall thereof with an interior coating characterized by the fact that the same is fluorescent and electrically conductive and translucent, the adjacent edge portions of said coatings overlap ping, and means for scanning the fluorescent coating.

6. A cathode ray tube including an electron source, a shield for said electron source, a first anode, a control electrode positioned in register and between said electron source and first anode,

a fluorescent screen and means, including said screen and a second electrode adapted to be maintained at a higher voltage relative to said source than said first anode for establishing a convergent electric field around the major por tion of the path traversed by an electron between said source and said screen, whereby electrons from said source may be focused to a well defined spot on said screen substantially independent of the potential of said control electrode.

VLADIMR K. ZWORYKIN. 

